Catalytic converters used in motor vehicles typically operate most efficiently at high temperatures. Upon starting the engine the catalytic converter temperature needs to rise sufficiently that it performs properly, a process commonly termed “light off”. “Light off” is normally defined as the temperature at which the catalytic converter reaches 50 percent efficiency. Depending on pollutant type, this typically occurs in a range of from about 200-300° C. One method of reducing light off time is to increase the temperature of exhaust gas arriving at the catalytic converter. To address this problem, and/or to protect sensitive vehicle components (for example, electronics, plastic parts, or the like) from heat given off by the vehicle exhaust, various double-walled exhaust system components (for example, exhaust manifolds, end cones for attaching to a catalytic converter, exhaust pipes, or pipes) have been developed. Such components generally have an inner pipe within an outer pipe. The annular gap formed between the inner pipe and the outer pipe may be left open or filled with an insulating material such as for example, a ceramic fiber mat.
Recently, there has been a trend toward the use of catalytic converters with diesel engines, which typically generate cooler exhaust gases than gasoline engines (for example, 200-300° C.). Accordingly, maintaining exhaust gas temperatures upstream of the catalytic converter is desirable in the case of diesel engines.
Effectively insulating a double-wall exhaust system component can be particularly challenging, for example, if the component has bends in it and/or if the annular gap formed between the inner and outer pipes is not uniform. This typically makes it difficult to fit anything in sheet form between the two pipes.